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Abstracts Brochure - CERN

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TUPCH — Poster Session 27-Jun-06 16:00 - 18:00<br />

functions. A client application can have access to the server data using the DOOCS application programming interface.<br />

A set of generic and specially devoted programs provide the tools for the operators to control the RF system.<br />

The RF operation at the linac is being automated by the implementation of DOOCS finite state machine servers.<br />

Phase and Amplitude Stability of the Next Generation RF Field Control for VUV- and Xray<br />

Free Electron Laser<br />

For pump and probe experiments at VUVand<br />

X-ray free electron lasers the stability of F. Ludwig, M. Hoffmann, H. Schlarb, S. Simrock (DESY)<br />

the electron beam and timing reference must<br />

be guaranteed in phase for the injector and bunch compression section within a resolution of 0.01 degree (rms) and in<br />

amplitude within 1 10-4 (rms). The performance of the field detection and regulation of the acceleration RF directly<br />

influences the phase and amplitude stability. In this paper we present the phase noise budget for a RF-regulation<br />

system including the noise characterization of all subcomponents, in detail down-converter, ADC sampling, vectormodulator,<br />

master oscillator and klystron. We study the amplitude to phase noise conversion for a detuned cavity.<br />

In addition we investigate the beam jitter induced by these noise sources within the regulation and determine the<br />

optimal controller gain. We acknowledge financial support by DESY Hamburg and the EUROFEL project.<br />

FPGA-based RF Field Control at the Photocathode RF Gun of the DESY VUV-FEL<br />

At the DESY Vacuum Ultraviolet Free Electron<br />

Laser (VUV-FEL) bunch peak current E. Vogel, W. Koprek, P. Pucyk (DESY)<br />

and the SASE effect are (amongst other parameters)<br />

sensitive to beam energy and beam phase variations. The electron bunches are created in an rf gun, which<br />

does not have field probes. Variations of the gun rf field cause beam energy and phase variations. They have a<br />

significant influence on the overall performance of the facility. DSP based rf field control used previously was only<br />

able to stabilize the rf output of the klystron. This was due to the lack of processing power and the over-all loop delay.<br />

The controller was not able to provide satisfactory rf field stability in the gun. Replacing the DSP hardware by the<br />

new FPGA-based hardware Simulation Controller (SimCon), we are able to reduce the latency within the digital part<br />

significantly allowing for higher loop gain. Furthermore SimCon provides sufficient processing power for calculating<br />

a probe signal from the forward and reflected power as input for PI and adaptive feed forward (AFF) control. In this<br />

paper we describe the algorithms implemented and the gun rf field stability obtained.<br />

Universal Controller for Digital RF Control<br />

Digital RF control systems allow to change<br />

the type of controller by programming of the S. Simrock (DESY) M.K. Grecki, G.W. Jablonski (TUL-DMCS)<br />

algorithms executed in FPGAs and/or DSPs.<br />

It is even possible to design a universal controller where the controller mode is selected by change of parameters. The<br />

concept of a universal controller includes the self-excited-loop (SEL) and generator driven resonator (GDR) concept,<br />

the choice of I/Q and amplitude or phase control, and allows for different filters (including Kalman filter and method<br />

of optimal controller synthesis) to be applied. Even time-varying mixtures of these modes are possible. Presented is<br />

the implementation of such a controller and the operational results with a superconducting cavity.<br />

215<br />

TUPCH188<br />

TUPCH189<br />

TUPCH190

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